1. Field of the Invention
The present invention relates to hearing aids. In particular, the present invention relates to a hearing aid having a microphone worn in the conchal bowl of the external ear, an amplifier and power source disposed behind the ear, and a sound conductor running from the housing behind the ear through the soft tissue of the external auditory canal and into the auditory canal medial to the cerumen-producing portion of the canal. The invention further relates to a method for installing said hearing aid.
2. Discussion of Background
The human auditory system includes the outer ear (the auricle or pinna), an auditory canal extending inwardly towards an ear drum or tympanum, a middle ear and an inner ear. The outer ear serves as a collecting dish for sound waves, which are then directed into the auditory canal toward the ear drum. Sound is perceived when the vibrations caused by sound waves are transmitted by the ear drum through the bones of the ossicular chain in the middle ear to the cochlea in the inner ear. The cochlea produces electrical impulses that are transmitted to the brain through the auditory nerve.
An estimated 15% of the population (about 40% of the elderly population) have impaired hearing and could benefit from the use of hearing aids. Most users of hearing aids are fitted with conventional aids of the "air conduction" or "bone conduction" type. Air conduction devices work by collecting incoming sound with a microphone, amplifying the sound and delivering the amplified signal by way of a speaker positioned in the outer portion of the ear canal. Amplifiers may be placed behind the ear or in the ear canal, as in the devices shown by Geers (U.S. Pat. No. 5,048,090) and Wullstein (UK Patent 962,780). Bone conduction aids convert the incoming sound signal into mechanical vibrations that are transmitted to the bone structure of the skull. The resulting vibration of the skull stimulates the cochlea, resulting in a perceived sound.
Implantable hearing devices offer some benefits in specific clinical situations but fail to meet the needs of the majority of those with hearing loss. Some implantable devices stimulate the temporal bone directly. Others vibrate the ossicular chain through various means such as a piezoelectric device or a magnet attached to one of the ossicles. Presently-available implantable devices include those described by Mahoney (U.S. Pat. Nos. 3,346,704 and 3,557,775), Branch (U.S. Pat. No. 3,764,748), Hough (U.S. Pat. No. 4,606,329), and PCT Application WO 89/05559. Implantable devices have been somewhat successful in overcoming problems such as acoustic feedback, but frequently require high power inputs. In addition, some implantable devices interrupt the normal hearing pathway by occluding the external auditory canal or interrupting the ossicular chain.
A number of problems are associated with presently-available hearing aids. In-the-ear or in-the-canal hearing aids block the external auditory canal and interfere with the user's remaining natural hearing, creating what is generally known as the "occlusion effect." These devices alter the acoustical characteristics of the auditory canal and often reduce the normal 8-10 dB amplifying effect of the concha (the central convexity of the external ear). Normal conductive hearing is decreased while bone conduction hearing is enhanced by approximately 9 dB, adversely affecting the user's perception of his own voice. This in turn may result in abnormal voice modulation. In addition, the amplified sound is frequently perceived as harsh and unpleasant due to a different frequency distribution from natural sound.
Children, the elderly and the handicapped may have difficulty with the tiny and/or complicated controls of some in-the-ear hearing aids, due to immaturity, lack of sufficient manual dexterity to manipulate the controls, or lack of sufficient ability to learn new skills. Such users are more successful in manipulating the controls of behind-the-ear aids.
Many users experience problems with acoustic feedback and background noise. Feedback is most evident in highly-miniaturized devices, an unavoidable consequence of the decreased distance from the speaker to the microphone. Poor signal-to-noise ratios result from the fact that hearing aids amplify signals indiscriminately, thus, amplified background noise may prevent a user from hearing and understanding the signal he or she wants to hear. By way of example, it may be difficult to distinguish a conversation from the background noise at a noisy cocktail party.
Of necessity, in-the-ear hearing aids are placed in the portion of the auditory canal that produces cerumen (ear wax), blocking the normal egress of cerumen, forcing it inwardly where it blocks the auditory canal as well as the vent and speaker ports of the aid. In addition, occlusion of the canal prevents the normal circulation of air, creating a "stuffy" sensation and predisposing the user to external ear infections. Some users develop an allergic response or intolerance when using an in-the-ear hearing aid constantly. Venting the device may partially overcome the occlusion effect, but may cause problematic acoustic feedback.
Candidates for hearing aids may refuse binaural fitting because of the cost or the occlusion effect. As a result, they have an imbalance in hearing from ear to ear, which results in difficulty with directional hearing. Devices that aim to provide directional hearing are available. For example, Davis (U.S. Pat. No. 5,239,588) mounts a stereophonic microphone on top of the user's head. Amplifiers are connected immediately adjacent to the microphone and subcutaneous wires connect the amplifiers to electroacoustic transducers in the ear canals.
Some users complain of discomfort when wearing a hearing aid, and many refuse to use one because of its association with aging or infirmity. When others notice that a person is wearing a hearing aid, they often speak in an abnormally loud voice which leads to discomfort. The less noticeable a hearing aid is to others, the more acceptable it is to its user.
Over the years, the size of hearing aids has diminished and their general quality has improved. However, there has been little significant improvement in hearing aid technology. Even the digitally programmable hearing aid, which offers the user some previously-unavailable flexibility in the frequency distribution of the amplified sound, does not represent a revolutionary change. Presently-available hearing aids do not satisfy the need of many potential users for an inconspicuous, easy-to-use device that provides adequate sound amplification with low acoustic feedback. Overall, only about 10% of those who might benefit from a hearing aid actually use one. Thus, a significant problem remains in helping those with hearing impairment. Perhaps the single most important incentive to increased hearing aid use would be an aid with an improved signal-to-noise ratio that uses rather than replaces the user's remaining natural hearing.